1. Field of the Invention
A vibratory wire displacement sensor of helical shape whose mode of vibration can be read out to indicate the displacement behavior between the anchored ends.
2. Description of Prior Art
The use of vibrating wire displacement gages per se is old as evidenced by such references as U.S. Pat. No. 3,675,474 to R. D. Browne. My invention employs a similar principle of operation but by using a different method of construction is able to provide a much more versitile sensor than the straight wire sensor. A straight wire of high tensile strength can elongate about 0.35 percent of its initial length before breaking. This restricts its use to what is known as the infinitesimal range in which displacements of the order of micro inches per inch are to be measured. If displacements greater than 0.35 percent are to be measured some other method is needed. This is commonly done with linear voltage differential transformers. These units are expensive when compared to the cost of a vibrating wire sensor. In addition, if straight wire sensors are used for small displacements and linear voltage differential transformers are used for large displacements, two readout systems must be purchased. In addition, the particular range of displacements is built into the linear voltage differential transformer. The helical wire sensor range and sensitivity can be established at the time of the test by the user. Because of the extremely low cost of the helical sensor it can compete commercially with any other displacement or strain sensor now on the market. The helical wire was tested with a low voltage plucking system owned by the United States Government entitled "Vibrating Wire Readout Meter". The readout meter was invented by William V. Bailey while working as a Creare Incorporated employee on a United States Bureau of Mines contract. This meter is disclosed in U.S. Pat. No. 3,889,525. The prior art stressed the need for the vibrating wire to be straight to avoid multiple readings in U.S. Pat. No. 3,411,347 to J. Wirth et al. In another U.S. Pat. No. 3,963,082 to Meier straight wire vibratory sensors are used for weighing purposes. In this patent a number of springs of helical shape are used to linearize the straight vibrating wire response. The straight wire sensors and not the springs are made to vibrate.